1. Technical Field of the Invention
This invention relates to an extension drilling system, and more particularly, but not exclusively, to extension drilling systems for use on a semi-automatic drilling rig and used to drill holes (bores) in subterranium mining operations such as coal mining where the structure of the roof of a tunnel is to be rendered more secure by the insertion of rock bolts into holes drilled into the roof structure.
2. Description of the Prior Art
In the past, extension drilling in coal mines was carried out using square threaded rods, such as XRT-Rods with a 4TPI Acme thread. We have experimented with the use of right-hand rope threaded drill rods because of their easier uncoupling and with a male thread less prone to damage. Although various extension drilling systems had been developed based on the experimental work, we have found that they did not work with semi-automatic drilling rigs.
The primary problem with conventional drill rods for extension drilling systems, when used with semiautomatic drill rigs is that, when the drill string (a series of drill rods coupled together) are to be uncoupled there are two threaded couplings between the grippers and the chuck. As the grippers are operated, and the chuck spun slowly in reverse, the threaded joint between the drive adaptor and the bottom extension rod can become uncoupled which is undesirable as distinct from the desired uncoupling between the bottom and second bottom extension rods.
A secondary problem is that the use of a drive adaptor takes up valuable boom height on the rig thus reducing the length of the extension rods that can be used.
It is therefore an object of the present invention to overcome, or at least minimize, the above problems with known extension drilling systems when associated with semi-automatic drilling rigs.